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When I was a child, I remember washing down a multivitamin and mineral (MVM) supplement with my orange juice each morning. That red pill fell into the same category as brushing my teeth, eating my vegetables and spending time outdoors—all daily activities somehow linked to health.

Apparently, I wasn’t alone. Supplement use is common in the United States: One-third of Americans take a daily MVM supplement, according to a 2011 study. The question is, why? Most people probably expect a daily multivitamin will make them feel better and prevent common illnesses, but evidence behind these claims is uncertain—does taking a daily multivitamin help boost resistance to disease, or does it do more harm than good?

Why Do We Take Multivitamins?

“Historically, vitamin and mineral supplements were used to prevent diseases caused by deficiency,” says Ann Diker, chair of the Health Professions Department at Metropolitan State University of Denver. Yet vitamin and mineral deficiencies aren’t common in the U.S. Today, Americans consume many processed foods, and much of it is fortified with vitamins and minerals—a report from the Centers for Disease Control and Prevention states that a fortification of foods with folate (a B vitamin) has reduced deficiency to less than 1 percent, and deficiency of vitamins A and E are also uncommon.

There are exceptions: For example, those living in poverty face food insecurity (unreliable access to high-quality food). Elderly people are generally more at risk for deficiency. Vegans often need to supplement with vitamin B12, Diker notes. Kids, menstruating women and pregnant women are more at risk for iron deficiency. Yet overall, the majority of us aren’t deficient in major nutrients. And if we are, it is a single deficiency.

So what’s our motivation for paying good money for MVMs? “Busy people don’t take the time to plan a diet that would supply all their vitamins and minerals,” Diker says. “So they take a MVM as a form of insurance.” What’s not clear is whether that insurance policy pays off.

Multivitamin Studies

A common expectation is that MVMs will prevent illnesses. However, most studies have not shown significant benefits in American adults. For example, in 2009 data from the Women’s Health Initiative (or WHI, a long-term national health study of postmenopausal women) judged that routine use of MVMs had no significant impact on longevity, the development of cardiovascular disease or several common cancers.

Multivitamins also appear not to benefit cognitive or cardiovascular health. Two studies published in the Annals of Internal Medicine in 2013 found that a multivitamin failed to improve cognitive function in older men and did not reduce cardiovascular events in patients after a recent myocardial infarction.

Yet multivitamins may help protect older people against cancer death. A 2013 study of postmenopausal women (ages 50 to 79) enrolled in the WHI found that, among women who had been diagnosed with invasive breast cancer taking MVMs around the time of diagnosis, the risk of death from breast cancer was 30 percent lower relative to women not taking MVMs.

Sylvia Wassertheil-Smoller, a doctor at Albert Einstein College of Medicine in Bronx, New York, was the principal investigator in both WHI studies. Her view is that MVMs don’t seem to benefit healthy people eating proper diets. However, due to biological and socioeconomic changes associated with aging, older adults are more at risk for inadequate nutrition. “Although the supplements didn’t prevent cancer, they may have helped these older women withstand the assault of cancer once it took hold,” Wassertheil-Smoller says.

A 2012 study followed 14,000 male physicians aged 50 and older for more than a decade and found that a daily multivitamin (Centrum Silver) reduced the number of new cases of cancer by 8 percent but did not impact the number of deaths.

When it comes to nutrients, more is not better. While deficiency can lead to ill health, excessive intake of some vitamins and minerals can be toxic—particularly fat-soluble vitamins such as vitamins A, E and K, which accumulate in the body. The Iowa Women’s Health Study evaluated the impact of a number of vitamin and mineral supplements on the risk of cancer, cardiovascular disease and death in older women over an 18-year period. A number of individual supplements such as iron and particularly copper were associated with an increased risk of death. Fortunately, MVMs were associated with a smaller risk. Lead researcher Jaakko Mursua, doctor at the Institute of Public Health and Clinical Nutrition, University of Eastern Finland, Kuopio, notes that most similar studies found no evidence for harm. In Wassertheil-Smoller’s studies, MVMs appear to be safe.

Should You Take a Multivitamin?

So should you take MVMs? The answer depends upon your age and state of health. “Children generally don’t need to take vitamin and mineral supplements,” says Mary Kohn, assistant professor of pediatrics at the University of Colorado. “Picky eaters may benefit from a daily children’s multivitamin to provide the vitamins they need and to avoid food battles. Exclusively breast-fed babies should receive 400 IU of vitamin D from age 2 months until they’re taking solid foods.”

All pregnant and breast-feeding women (and those planning pregnancies) should take prenatal vitamin supplements that contain folic acid, crucial for proper nervous system development, says Kate Koschoreck, nurse-midwife at the University of Colorado. Wassertheil-Smoller’s attitude for adults older than 50 is, “These multivitamins do no harm and may do good if a women develops breast cancer. So why not take them?”

Healthy, well-nourished adolescents and adults don’t usually need MVMs. Most health professionals say whole foods trump supplements every time because food—particularly plant food—is chemically complex, containing much more than the vitamins and minerals you get in a pill. If you have any doubts, consult your doctor. Tests can determine whether you are deficient in a particular vitamin or mineral.

Other Dietary Supplements

This article only addresses multivitamin and mineral formulas. A host of other supplements exist: single vitamins and minerals, amino acids, essential fatty acids, hormones, herbal extracts and more. These supplements may be appropriate to help treat or prevent certain illnesses or conditions. Consult your physician.

Linda B. White, M.D. works as a lecturer and freelance writer. Her most recent books are Health Now: An Integrative Approach to Personal Health (Flat World Knowledge, 2013) and 500 Time-Tested Home Remedies and the Science Behind Them (Fair Winds Press, 2014), which was coauthored with Barbara Seeber and Barbara Brownell Grogan. She also blogs regularly with The Remedy Chicks, and can be found on Twitter @drlindawhite.

It makes a difference whether vitamins are synthetic or derived from natural sources. Most studies do not consider this issue. Many physicians do not know the difference. Also, absorption rates differ between different types of tablets and capsules...and different individuals and the condition of their digestive systems. Listen to your body, read labels, and do your homework.

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